<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>派生类选择器</title>
    <style type="text/css">
        p .font{
            color: blue;
            border-bottom: red 10px solid;
        }
    </style>
</head>
<body>
<p>
    你干啥？
    <a class="font">不好了</a>
</p>
</body>
</html>